The principal positively charged ion that has a significant role in maintaining fluid and electrolyte balance is

potassium (K⁺)

Explanation:

1) To answer this quesiton you need to know the context of the same.

2) This questions is referred to the metabolism: the reactions that occur inside the body.

3) The potassium is the principal positively charged ion (cation) that has a main role in mantaining fluid and electrolyte balance in the organism.

4) Electrolytes are ionic compounds in aqueous solutions.

5) An adequate balance of electrolytes in the organisms is necessary for the normal function of the cells and organs.

6) There are two major positive ions in our organism, sodim (Na⁺) and potassium (K⁺). While sodium is the major positive ion outside the cells, potassium is the major positive ion inside the cells.

Outermost (valence) electrons